The invention relates to a non-contacting hydro-dynamic seal for rotary machines which can be applied both to shaft- and to end-face seals. It relates particularly to a seal with very low friction losses.
There exist two kinds of non-contacting seals up to date:
1. The labyrinth seal which consists of a plurality of interengaging circular cams and grooves respectively provided on the rotating and the stationary part of the machine, PA0 2. The screw-type seal which comprises a projecting ridge wound around a rotating shaft with a narrow gap remaining between the stationary casing and the shaft, the seal operating in the fashion of an Archimedean Screw by pumping fluid towards the high-pressure side of the machine, and PA0 3. The so-called film-riding seal wherein a rotating surface rides on a liquid or gas film of minute thickness and is controlled by pressure screws incorporated in the face design. This seal is useful where very high pressures are encountered, in machines wherein extreme temperatures and specific materials do not permit any rubbing contact.
A fourth kind of hydro-dynamic seal has been conceived lately which utilizes the fluid friction in a narrow gap between a moving and a stationary part to pump fluid into an area surrounded by a ridge of different height whereby the gap between the parts is larger in all points of the ridge where the relative velocity vector extends into that area, and smaller in all points where it extends out of the area.
Whilst the three first mentioned seals permit a certain percentage of fluid to escape into the open, there are not sufficient data available in respect to the third seal, so as to make an evaluation of its properties and its efficiency possible.
The invention is based on the mathematical theory of lubrication developed by Osborne Reynolds which has led, inter alia, to the understanding and construction of hydrodynamic bearings. A typical hydrodynamic thrust bearing comprises a flat, smooth rotor and a stator consisting of radially distributed pads, the surfaces of these pads being aligned so as to form a predetermined angle with the rotor surface. The motor velocity relative to the pad surface creates a high-pressure zone, associated with an enhanced flow rate, in the gap between the rotor and the pad surfaces.
This principle has been extended, although in different form from the construction of the aforesaid thrust bearings, to the design of both axial and radial seals for rotating machines wherein the outflow of a liquid through the gap between a rotating and a stationary part is to be prevented.